An integrated and automated measurement system of the static extinction ratio of crystal, the static or dynamic extinction ratio and half wave voltage of electro-optic crystal and the phase retardation of a wave plate is studied. By using the interferometric technology of polarized light, the pulse-modulated light source, the demodulation circuit and the division routine in computer program, the system effectively combines optics, mechanics and electronics technologies with computer control technology, which can be used to measure the above-mentioned three parameters fast, synthetically and automatically not only for laboratory research but also for product line. The results prove that with the measurement theory and the method of the paper, the extinction ratio of crystal can be measured to 10-6 , and the repeat accuracy of the phase retardation of a wave plate can be measured to excel 0.3° ; moreover, by using the longitudinal modulation technology of the electro-optic crystal, the half-wave voltage of crystal can be measured accurately.